Heat exchangers such as radiators to be mounted in automobiles are produced by assembling tube members and fin members, each formed from brazing sheets composed of aluminum alloys; and brazing these members to give an assembly. For reducing the weights of such heat exchangers, the aluminum alloy brazing sheets have had a smaller and smaller gage, whereby have been required to have higher strength and higher corrosion resistance. For example, common aluminum alloy brazing sheets for tube members have a reduced sheet thickness of about 0.17 mm, whereas former ones have had a sheet thickness of about 0.20 mm.
There are known techniques relating to aluminum alloy brazing sheets excellent in corrosion resistance. Typically, Patent Document 1 discloses an aluminum alloy brazing sheet of a three-layer structure including an Al—Mn—Cu alloy core material, an Al—Zn alloy sacrificial anode material (clad material) lying on one side of the core material, and a filler material lying on the other side of the core material. A sacrificial effect can be imparted to the clad material by cladding a Zn-containing clad material on one side of a Cu-containing core material as above. The resulting laminate is formed into a tube member so that the clad material faces inward, to thereby improve the corrosion resistance against the coolant passing through inside the tube member. Additionally, the brazing sheet as the tube member is suitable for brazing with a fin member, because the filler material is cladded on the other side of the core material, i.e., on the outer surface of the tube member.
One of factors important to improve the corrosion resistance of the brazing sheet is erosion resistance, by which the erosion of the brazing filler into the core material during brazing of the brazing sheet is suppressed so as to prevent the core material from locally reducing its thickness. Typically, Patent Document 2 discloses a technique in which crystal grain boundaries of the core material are decreased by controlling the average grain size of the core material after brazing to 300 μm or more, because such crystal grain boundaries often allow the brazing filler to enter therethrough into the core material.
Patent Document 1: Japanese Patent No. 3536065 (Paragraphs 0007 to 0012)
Patent Document 2: Japanese Unexamined Patent Application Publication (JP-A) No. 2004-17116 (Paragraphs 0007 to 0008)